AUSTIN — Powered by what's expected to be continued vibrant sales tax collections, lawmakers will have $119.1 billion to spend as they get down to the nitty-gritty of crafting the state's two-year spending plan, Texas Comptroller Glenn Hegar said.

"The (Texas) economy has been doing very well lately," Hegar, the state's chief financial officer, said as he unveiled the official revenue estimate that will guide the budget-writing process when the Legislature convenes for its 140-day session on Tuesday. "The economy has been extremely robust."

The forecast is 8.1 percent above what lawmakers had to spend two years ago.

By the numbers

Hegar's forecast, which must see more than two-and-a-half years into the future, is based on the expectation that sales tax collections will top $66 billion between now and Aug. 31, 2021. That's a 9.5 percent increase.

That sounds like a large spike, but Hegar said it's actually slightly slower than the double-digit increases Texas has seen during the past several years. Sales taxes make up nearly 55 percent of the revenue raised by the state.

The taxes collected on the sales of new cars, trucks and manufactured housing units, meanwhile, will likely drag behind what Hegar's office had anticipated a few years ago.

The state's Rainy Day Fund, which is sort of state savings account that is powered by a portion of the taxes collected on oil and gas production, is likely to grow from its present balance of about $12.5 billion to about $15.4 billion.

But Hegar was quick to point out that his forecast does not take into account how much lawmakers might decide to spend from the savings, so the balance at the end of the 2020-21 budget will likely be less.

There's always uncertainty

Hegar said although oil and gas taxes tend to increase by an annual average of 7 percent, the year-to-year fluctuations are far more dramatic. For instance, oil and gas taxes tanked about 40 percent in 2016. But they were up about 60 percent two years later.

That's one of the reasons Hegar described his forecast as "cautious" and may well be revised as the outlook becomes clearer.

Also, Gov. Greg Abbott and some legislative leaders say they hope to lower the growth in local school property taxes, which could shift to the state a larger share of the cost for public schools. It remains an open question whether the goal can be accomplished by the Legislature, and whether the increase in revenue is sufficient for the state to meet that burden.

What they are saying

“Today’s revenue estimate reflects the continued strength of the Texas economy." Abbott said. "Even with this strong economic growth, Texans expect their government to live within its means, while funding its priorities."

"We face a broad range of fiscal challenges in the 86th Legislative Session," he added. "and we are committed to property tax reform, increasing teacher pay and school finance reform. We are confident we can accomplish these goals."

Texas Democrats, who picked up 12 House seats and two in the Senate in the November elections but still remain in the minority in both chambers, said the uptick in state revenue presents an opportunity to boost school funding.

"Today's revenue estimate shows that the Legislature should fund a significant, added investment in public education, which in turn would reduce pressure on property taxpayers," said House Democratic leader Chris Turner of Arlington.

"Texas teachers deserve better pay and we need to address health care costs for current and retired educators," he added. "We need to make college more affordable and accessible if we are to have the skilled workforce our state’s economy demands."

More money, unmet needs in the present budget

Hegar said that by the time all dollars come to the state during the present budget cycle, total revenues should be about $4.2 billion more than expected when the 2017 Legislature passed its two-year spending plan.

But the lion's share of that will likely be gobbled up by costs associated with recovery from Hurricane Harvey and from growth in the Medicaid program, which provides health coverage to qualifying low-income Texans.

John C. Moritz covers Texas government and politics for the USA Today Network in Austin. Contact him at John.Moritz@caller.com and follow him on Twitter @JohnnieMo.